The present invention relates to an element having a three-dimensional structure that is formed accurately on a substrate such as a silicon wafer using a sacrificial layer and a method of manufacturing the element. In particular, the invention relates to an optical switch that is formed using a sacrificial layer and a method of manufacturing the optical switch.
In recent years, a method of forming a sacrificial layer on a substrate such as a silicon wafer, forming a thin film structure patterned in a desired shaped on the sacrificial layer, and thereafter forming a desired three-dimensional structure by removing the sacrificial layer has been attracting attention. Since it is possible to form a large number of fine three-dimensional structures accurately and at a high density with this method, the method is suitable for manufacturing a spatial light modulation element and the like.
As a method of removing the sacrificial layer present between the substrate and the thin film structure in such a method of manufacturing a three-dimensional structure using a sacrificial layer, Japanese Patent Laid-open Publication No. 2001-13426 and Japanese Patent Laid-open Publication No. 2001-129798 disclose use of a solution for wet etching such as a hydrofluoric acid water solution. However, in the solution for etching like the hydrofluoric acid water solution that uses water as a solvent, a phenomenon in which water molecules adhere to the thin film structure at the time of etching and the thin film structure adheres to the substrate due to a surface tension of the water molecules tends to occur. When the fine thin film structure adheres to the substrate once, it is not easy to peel off the thin film structure. Thus, the thin film structure may keep adhering to the substrate after drying, making it impossible to obtain a desired three-dimensional shape. In particular, when a thin film structure of a three-dimensional shape including a movable portion is formed, if the thin film structure adheres to a substrate, a function of the movable portion cannot be performed.
On the other hand, as another method of removing a sacrificial layer, a method of removing a sacrificial layer with a dry process such as ashing has been proposed. For example, when the ashing is used, it is known that an organic resist film is used as the sacrificial layer.